Consider the boiler in Problem 9.21 where the geothermal hot water brings the R-134a to saturated vapor. Assume a counterflowing heat exchanger arrangement. The geothermal water temperature should be equal to or greater than that of the R-134a temperature at any location inside the heat exchanger. The point with the smallest temperature difference between the source and the working fluid is called the pinch point. If 2 kg/s of geothermal water is available at 95◦C, what is the maximum power output of this cycle for R-134a as the working fluid? (Hint: split the heat exchanger C.V. into two so that the pinch point with ΔT = 0, T = 85◦C appears.)

Data from Problem 9.21

A supply of geothermal hot water is used as the energy source in an ideal Rankine cycle with R-134a, as shown in Fig. P9.21. Saturated vapor R-134a leaves the boiler at a temperature of 85◦C, and the condenser temperature is 40◦C. Calculate the thermal efficiency of this cycle. 

Transcribed Image Text:

Pinch point 2 R-134a+ D Liquid heater R-134a 85°C Boiler B H,0 95°C FIGURE P9.65